Atrial fibrillation is a common arrhythmia becoming increasingly frequent as patients advance in age. It is associated with a multiplicity of symptoms including fatigue, weakness, syncope, congestive heart failure, and strokes. It is a major cause of hospitalizations and of morbidity resulting in a significant economic burden to the individual and society.
Numerous therapies have been advanced to terminate accelerated atrial arrhythmias such as atrial fibrillation or organized atrial tachyarrhythmias such as atrial flutter. For example, high rate or overdrive pacing of the atria has shown to be effective in some cases to terminate atrial flutter. For atrial arrhythmias which advance to the more chaotic atrial fibrillation, overdrive pacing may still be effective in some cases. Atrial defibrillation, which entails delivering a brief cardioverting electrical shock to the atria, has also been found to be effective in some cases.
Before a therapy can be delivered, the arrhythmia itself must first be detected. Generally, such detection involves the sensing of high rate intrinsic atrial beats, whether they are normal (slight acceleration of a normal sinus rhythm) or premature and ectopic. However, such detection is not totally effective and even when found to work well in a given patient, rate changes alone may not be an adequate precursor in every instance. This suggests that there is more that is transpiring at the atrial muscle layer or cellular level than has been identified to date. If the earliest precursors are missed, later therapy may be inadequate to terminate the arrhythmia.
It has been shown that the longer that patients are in normal sinus rhythm, the more likely it is that they will stay in normal sinus rhythm. Hence, it would be most advantageous if an impending accelerated atrial arrhythmia could be identified and then upon such identification, preventative therapy delivered to the patient to keep the patient's atrial arrhythmia from developing and maintaining the patient in normal sinus or stable atrial paced rhythm. The present invention addresses these issues.